In large, heavy saucepan, combine scallops, wine, salt, and pepper. Bring slowly to boil and simmer gently for 5 minutes. Drain. Set cooking liquid aside for further use.
In same saucepan, melt butter. Add onions and cook over low flame for 10 minutes. Add mushrooms, parsley, tomato pastetomato paste, and 1 and a half tablespoons of bread crumbs. Bring to boil. Simmer gently for 5 minutes, or until sauce is thick and well blended.
Cut scallops into small pieces and return to pan. Fill buttered shells or individual casseroles with scallop mixture. Sprinkle with remaining crumbs. Dot with butter. Broil under broiler flame until top is golden. Serve hot.